Acoustic devices for time-multiplexed communication

ABSTRACT

A transmitter for time-multiplexed communication, utilizing complementary non-interacting codes, comprising: an acoustic surface-wave device, which provides two parallel signal propagation paths on its surface; a first signal source for generating an intermittent stream of pulses; a second signal source for generating a stream of pulses in the intervals of time when the first signal source is not generating a stream of pulses; a signal source switch; a multiplexing double-pole, double throw switch, for alternately switching a pair of output signals from the acoustic surface wave device between two transmit channels; a timing and control apparatus connected to the first and second signal sources and to the signal source and multiplexing switches, which controls (1) the time periods, or intervals, during which the first and second signal sources are alternately energized, and (2) the switching of the arms of the switches from one position to the other in synchronism with the alternate energization of the signal sources; with the result that a stream of intermittent pulses from the signal sources becomes a more or less continuous pair of signals. The first of which is sent over one transmit channel and then the other transmit channel, as determined by the timing control, while the second is sent on the two transmit channels in alternate order, the streams of output signals concealing coded information. A receiver for time-multiplexed communication, having similar components, is also described.

[ ACOUSTIC DEVICES FOR TIME-MULTIPLEXED COMMUNICATION [75} Inventor:James M. Alsup, San Diego, Calif.

\[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

{22] Filed: July 1, 1974 l[2l] Appl. No: 484,490

[52] 1.1.3. C1. 179/15 BC; 178/22; l79/l.5 R; Il79/l5 A; 333/30 R;333/30 R;7O T;71;72 [51] Int. Cl. H04k 1/10 {58] Field of Search 179/15BC, 1.5 R, 1.5 S, 1179/15 A; 178/22, 99

[56] References Cited UNITED STATES PATENTS 3,551,837 12/1970 Speiser l333/30 R 3,723,916 Ill/1973 Speiser 333/30 R 3,833,867 ii/1974 Solie333/30 R Primary Examiner-David L. Stewart Attorney, wlgent, 0rFirmRichard S. Sciascia; Ervin F. Johnston; l'ohn Stan l 5 1 ABSTRACT Atransmitter for time-multiplexed communication,

[ June 11), 1975 utilizing complementary non-interacting codes,comprising: an acoustic surface-wave device, which provides two parallelsignal propagation paths on its surface; a first signal source forgenerating an intermittent stream of pulses; a second signal source forgenerating a stream of pulses in the intervals of time when the firstsignal source is not generating a stream of pulses; a signal sourceswitch; a multiplexing doublepole, double throw switch, for alternatelyswitching a pair of output signals from the acoustic surface wave devicebetween two transmit channels; a timing and control apparatus connectedto the first and second signal sources and to the signal source andmultiplexing switches, which controls (1) the time periods, orintervals, during which the first and second signal sources arealternately energized, and (2) the switching of the arms of the switchesfrom one position to the other in synchronism with the alternateenergization of the signal sources; with the result that a stream ofintermittent pulses from the signal sources becomes a more or lesscontinuous pair of signals. The first of which is sent over one transmitchannel and then the other transmit channel, as determined by the timingcontrol, while the second is sent on the two transmit channels inalternate order, the streams of output signals concealing codedinformation.

A receiver for time-multiplexed communication, having similarcomponents, is also described.

6 Claims, 5 Drawing Figures Cam-20L a 5% fxm/vsM/rrEQ Fae me Gem/sienna0/: TWO M04 TIPLE'XED EA/00529 VGA/AL ll ACOUSTIC DEVICES FORTIME-MULTIPLEXED COMMUNICATION STATEMENT OF GOVERNMENT INTEREST Theinvention described herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to improved, acousticdevices for time-multiplexed communication or ranging with complementarynon-interacting codes. The invention describes means for using a singlepair of electrode structures to serve as a generator of or matchedfilter for two non-interacting pairs of Golay complementary sequences.

Prior art methods for implementing generators or matched filters for anumber of Golay pairs exceeding one required as many pairs of electrodestructures (or more) as pairs of sequences.

The implementation herein disclosed reduces the complexity pt electrodefabrication by two, with related gains in size, ease of manufacture. andsimplicity. The only offsetting factors are a slight reduction inavailable data rate and a slight increase in signal switchingoperations.

For background information on this invention and on the prior art,reference is directed to the article entitled Surface Wave TransducerArray Design Using Transversal Filter Concepts," by .l. M. Speiser andH. J. Whitehouse, in the book entitled Acoustic Surface Wave andAcousto-Optic Devices, edited by T. Kallard, Optosonic Press, NYC, NY,197i, and to US. Pat. No. 3,723,916, Surface Wave Multiplex TransducerDevice With Gain and Sidelobe Supression, to J. M. Speiser, et al.,which isssued on Mar. 27 1973.

SUMMARY OF THE INVENTION A single, matched-filter pair is used to encodeor decode two independent, time-multiplexed signals. The matched-filterpair consists of a dual-channel acoustic delay line such that onechannel has a distributed tapping structure T,, which represents Code A,of a coded complementary pair, while the second channel has a similartapping structure T representing Code B, of the same coded complementarypair. Single-tap transducers located at both ends of the multi-taptransducer structures are used to launch (or receive) acoustic signalsto (or from) these structures.

In brief, the system operates as follows:

A group of pulses, generated by a signal source, corresponding to adesired message are fed into a pair of single-tap transducers. If eachtransducer, T and T has I6 :sets of fingers, for example, each inputpulse generates a pair of output signals each comprised of 16 pulses (orsamples).

The signals are transmitted over the two channels, and then they arereceived and put into the two separate channels of the receiving matchedfilter, which is identical to the one in the transmitter except that thesignals are put in from the other end, with respect to the single-taptransducers. Out of the receiver come a pair of autocorrelationfunctions which, when summed, comprise the stream of pulses originallyentered into the transmitter, that is, the message.

The signal source may generate pulses so rapidly that the output signalscorresponding to adjacent input pulses may overlap each other.

Now, if a second signal source is energized, the first signal sourcemust be allowed to die out first, so that the signals generated by thetwo would not overlap.

The time spread between output signal pulses (or samples) is determinedby the acoustic delay between transducer taps. An upper bound on thefrequency of input pulses from a signal source is obtained bycalculating the inverse of this intertap delay.

With respect to the sequencing of the two signal sources, one signalsource could be energized for one second, then the second signal sourcefor one second, and thereafter multiplexing in alternation.

Or a previously agreed upon scheme could be used whereby one signalsource would be used most of the time, until two signals had to be sentsimultaneously. The person receiving the signal generated by the firstsignal source could be advised that signals from the second signalsource are about to be transmitted, or the manner in which thesequencing is to be done could be agreed upon in advance.

A matched-filter pair of the type described can be constructed usingacoustic surface-wave techniques, acoustic torsional-wavemagnetostrictive-wire techniques, or any means whereby signals can bepropagated through the distributed tapping structures simultaneously inboth directions.

The type of coding or decoding achieved is a convolutional superpositionor extraction of adjacent pulses in the signal source. A description ofa means for generating a pair of such time-multiplexedconvolutionallyencoded signals using an acoustic surface-wave devicefollows. When the first signal source is activated, it drives single-taptransducers T and T at one end of the surface-wave device, with a trainof pulses which propagate in a bandpass acoustic format towards thecorresponding multi-tap transducers T and T The corresponding electricaloutput from transducer T A is transmitted over transmit channel No. 1,and that from transducer T is transmitted over transmit channel No. 2.

When the second signal source is activated, it drives single-taptransducers T and T at the other end of the surface-wave device, withits train of pulses. In this case, the corresponding electrical outputfrom transducer T,, is transmitted over transmit channel No. 2, and thatfrom transducer T over transmit channel No. 1. If transducers T and Tare in phase, then transducers T and T should be of opposite phase (orvice versa) to achieve the non-interacting property. Signals aretime-multiplexed so that convolutionallyencoded signals originating fromthe first signal do not overlap, in the time domain, theconvolutionallyencoded signals originating from the second signalsource.

Decoding is accomplished by the same or by an identical device(depending upon whether echo-ranging or communications is theapplication). The receiver for decoding can be operated in either of twomodes: either/or mode selects either to decode the signal generated bythe first signal source, or the signal generated by the second signalsource; multiplexed output mode decodes both signals but does notperform demultiplexing.

R R 8 (T) and R n R -'1 0.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, thisfigure illustrates an The term R designates the autocorrclation function5 acoustic surface'wave device 10, which provides two of coding A: R theautocorrelation function of coding 8; R is the cross-correlationfunction of coding A and the reverse of coding B; while the term R n isthe cross-correlation function of coding B and the reverse of coding A.The term 5 (T) relates to the Dirac delta function.

The principle just illustrated can be extended to hold for a number n oftimemultiplexed signals, with the number of acoustic paths on the deviceand the number of propagation channels required also increasing, insteps of 2'", n 2'". However, the real advantage of utilizing thebidirectional acoustic delay lines to implement two codes with a singlemutli-tap transducer structure occurs when the number of signals to bemultiplexed is exactly two.

A specific application for two-signal multiplexing is for pulsecodemodulation (PCM) communication in which each sample of the signal to becommunicated is represented in a serial-bit format. These bits are usedto pulse (1) or not pulse the input to the encoder, but a frame pulseevery k'" sample (k an integer I) is always required. The frame pulse,then, may be the second signal source, and can be selected to appear atthe receivers output for initial synchronization, and after a suitable(short) interval, the receiver can be switched into the multiplexedoutput mode.

OBJECTS OF THE INVENTION An object of the invention is to provide atimemultiplexed communication which utilizes half as many electrodestructures as prior art devices.

Another object of the invention is to provide a time-multiplexedcommunication which has much greater gain than similar prior artdevices.

Yet another object of the invention is to provide a time-multiplexedcommunication which is much simpler in construction than prior artdevices.

Other objects, advantages and novel features of the invention willbecome apparent from the following de tailed description of theinvention, when considered in conjunction with the accompanyingdrawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of anacoustic surfacewave device for two-signal multiplexing, utilizing onepair of transducers coded according to the two members of acomplementary pair;

FIG. 2 is a schematic diagram of an implementation of a transmitter forthe generation of two multiplexed encoded signals.

FIG. 3 is a schematic diagram, similar to FIG. 2, of an alternateversion of an implementation of a transmitter for the generation of twomultiplexed encoded signals.

FIG. 4 is a schematic diagram ofa receiver to be used with thetransmitters, shown in FIGS. 2 and 3, of two encoded signals, notnecessarily multiplexed, in an either-or" mode.

FIG. 5 is a schematic diagram of another type of receiver, which can beused also with the transmitters shown in FIGS. 2 and 3, in a multiplexedoutput mode."

parallel, horizontal, signal propagation paths on its surface, used in atransmitter for time-multiplexed communication, utilizing complementarynon-interacting codes. The surface-wave device It) comprises a substrateI2, capable of propagating acoustic surface waves. A pair of codedinterdigited electrode structures, I4 and I6, are disposed upon thesubstrate I2, one structure in each of the propagation paths, onestructure coded according to one member ofa complementary pair, theother structure coded according to the other member of a complementarypair, each coded electrode structure transdueing an acoustic wavepropagating in its respective propagation path into an output electricalsignal which may be transmitted externally off the substrate by means ofoutput leads. For every electrical pulse impressed upon transducer 17L,a stream of pulses, corresponding to the coding A on transducer 14, isgenerated by transducer I4. A similar situation obtains with respect totransducer 18L and I6.

Alternatively, if T, and T,, are used as input transducers, then theexcitation of them by an electrical pulse results in a pair of acousticsignals representing the signals A and B propagating in the upper andlower channels, respectively, of surface wave device 10. When receivedby transducers I7L and 18L, respectively, these acoustic signals becomeelectrical signals suitable for transmission over a pair of transmitchannels.

Coded transducers I4 and 16, also designated as T, and T are codedaccording to the two members A and B of a complementary series, a Golaycomplementary series, as illustrated.

Because the transducers 14 and 16 are shown for use in a narrow-bandsystem, for example a five percent bandwidth, the coded electrodes donot require a fielddelineating electrode interposed between the twoelectrodes shown. In a wideband system, for example bandwidth,field-delineating electrodes would be required. These are described inan issued patent.

As mentioned hereinabove, electrodes configured according tocomplementary codes are involved in surface wave transducers I4 and 16.A specific complementary code from which useful results were obtainedwas a Golay complementary code. Useful background information onsurface-wave devices in general and specifically on Golay codes may beobtained from US. Pat. No. 3,551,837, to J. Speiser, et al., whichissued on Dec. 29, 1970 and is entitled Surface Wave Transducers WithSide Lobe Suppression."

Two pairs of individually uncoded interdigitated electrode structures,I7L, 17R and I814, 18R are disposed upon the substrate I2, one pair ineach of the two propagation paths on each side of the coded electrodestructures, Id and 16. For non-interacting code operation, one of theseuncoded electrodes (17L, 17R, ISL, 118R) can be specified to haveopposite carrier phase from the other three, resulting in the negationof the signal leaving or entering that electrode structure.

The acoustic surface-wave device 10 has the property that a singleelectrical pulse applied to an uncoded electrode structure I'7L, 17R orISL, ISR, results in a multiple-pulse (or multiple-sample) electricaloutput signal at the output leads or bus bars, of transducer 14 or 16.

Referring now to FIG. 2, this figure shows a first signal source 22 forgenerating pulses, whose output is connected through a switch 26 to twoof the uncoded electrode structures 17L and 18L, (FIG. 1), which are onthe left side of the coded electrode structures, 14 and 16,respectively, the signal source generating a stream of input pulses.

A second signal source 24, also for generating input pulses, has itsoutput connected, again through switch 26, to the other two uncodedelectrode structures 17R and 18R, and generates a stream of input pulsesin the intervals of time when the first signal source is not generatinga stream of input pulses.

An input pulse from the first signal source 22 results in thetransmission of a +A signal on transmit channel No. l and +B signal ontransmit channel No. 2, whereas an input pulse from the second signalsource 24 results in the transmission of a B signal on transmit channelNo. l and a +A signal on transmit channel No. 2, with the coding shownfor transducers 17L, 17R, 18L, and 18R. One method of obtaining a signalB from a signal +B is to invert the carrier, and one way to invert thecarrier is to invert the polarity of transducer 18R, with respect totransducers 17L, 18L and 17R.

Signals generated by the first signal source 22 and the second signalsource 24 comprise pulses, either coded or uncoded.

Assume that transducers 14 and 16 are coded, for example according to al6-sample Golay code. For every pulse applied to either transducer 17Lor 18L, there would be l6 code samples coming out of each codedtransducer (14 and 16, respectively) for each code bit coming in.

If a next incoming code bit is applied after the 16 code samples havebeen produced at the output of the transducer 14 or 16, a time delaydependent upon the acoustic propagation time between first and last tapsin the transducer 14 or 16, then there will not be an overlap in the twol6-sample sets.

If an input pulse appears before all 16 samples have been produced bythe transducer structures, then some of the 16 output samples generatedby the second input pulse will overlap the 16 output samples generatedby the first input pulse. This is not only allowable, but is, in fact,desirable.

When these output samples enter a receiver, which will be described inconnection with FIGS. 4 and 5, even though some may overlap, thereceiver deconvolves the two sets of samples, so that what comes out ofthe receiver is the original sequence of pulses which were emitted bythe first or second signal source, 22 or 24, to excite the transmitter.Effectively, the samples which had overlapped, now no longer overlap,and are now resolved.

A typical application of the invention is in spread spectrum devices.The input sequence of pulses are spread out by the device so that theyoverlap each other, so that an unauthorized individual who is listeningto the signal sees a group of samples which are all jumbled up, that is,would only see an indecipherable mixture of samples, and probably noteven know that there is a coded signal in the mixture. A system such asthis is sometimes called a partially covert system.

Referring back to FIG. 2, the transmitter also comprises a multiplexingdouble-pole, double-throw switch 28 for alternately switching an outputsignal from each of the coded electrical structures 14 and 16, to eachof two transmit channels, over leads 32 and 34. In FIG. 2, the leadsdesignated from T and from T actually involve two wires, one connectedto one of the top bus bars of electrode structure 14 and one connectedto one of the bottom bus bars of electrode structure 16. One of the twoleads would generally be connected to a neutral point.

A timing and control apparatus 36 is connected to the first and secondsignal sources 22 and 24, and to the signal source and multiplexingswitches, 26 and 28. It controls l) the time periods or intervals,during which the first and second signal sources 22 and 24, arealternately energized, and (2) the switching of the arms of the switches26 and 28, from one position to the other in synchronism with thealternate energization of the signal source. It will be noted FIG. 2shows one switch position for one source 22 of multiplex signaltransmission, while for the other source 24 of signal transmission, theswitch arms of switches 26 and 28 would both be reversed.

The result is that a stream of intermittent pulses from the signalsources 22 and 24 become a pair of more or less continuous streams ofsamples which are sent via two transmit channels, with channel exchangeoccurring at intervals determined by the timing control, the stream ofoutput samples concealing coded information, if desired.

In transmitter 20, shown in FIG. 2, the pair of coded, interdigitated,electrode structures, 14 and 16 in FIG. 1, may be coded according to thetwo members of a Golay complementary pair.

Referring now to FIG. 3, this figure illustrates another embodiment of atransmitter 40 for timemultiplexed communication, utilizingcomplementary non-interacting codes, including the same type of anacoustic surface-wave device 10 as is shown in FIG. 1.

The transmitter 40 also includes a first signal source 22 for generatingan intermittent stream of pulses and a second signal source 24 forgenerating pulses in the intervals of time when the first signal sourceis not generating a stream of pulses.

A signal source switch 42 has its terminals connected to the outputs ofthe first and second signal sources 22 and 24, its switch arm connectedto each of the coded electrode structures, 14 and 16 in FIG. 1.

A multiplexing double-pole, double-throw switch 50, alternately switchesan output signal from each pair of the uncoded electrode structures,17L, 18L or 17R, 18R, in FIG. 1, to each of two transmit channels, overleads 44 and 46. The switch 50 comprises: one pair of terminals 52connected to one of the pairs of uncoded electrode structures, 17L and18L; the other pair of terminals 54 being connected to the other pair ofuncoded electrode structures, 17R and 18R; with the two switch arms 56being connected to the two transmit channels over leads 44 and 46.

In FIG. 3, for the position shown of the switch arm of switch 42, theswitch arms 56 of switch 50 could be making contact with terminals 54,rather than terminals 52 as shown, and the transmitter 40 would stilloperate properly.

A timing and control apparatus 48 is connected to the first and secondsignal sources, 22 and 24, and to the signal source switch 50. Thecontrol 48 controls (1) the time periods or intervals, during which thefirst and second'signal sources 22 and .24, arealternatciyenergized;-and (2). the switching of the arms 56 of the figured as atransmitter (FIG. Zor-FIG; 3)-or'as are- I ceiver.( FlG. dor F165). I II I To give a general description of the operation and 021- pabilitiesofthe transmitter-receiver combination, as

' I .nalsource is used to input message pulses in a FCll/lfon' mat'atother sample positions in the frame. When the which are sentvia'twotransmit channels on: leads M- I and. d6, withchannel; exchangeOccurring at intervals. I determined by the timing control 48, thestream o'f'output samples capable of concealing'codeclinformation..- I

Referring now to FIG. 4,: thisfigureillustrates a receiver 60-fortime-multiplexed communication, utiliz ing; complementarynon-interacting codes, comprising an acoustic surface-wavedevice,similar to the one la- I beled in FIG. l. I l I The receiver 60also. includes areceived signai switch .7fl, comprising: a. pair ofswitch arms 72,- each arrn I 7 being connecta-ble to a signal receivedfrom a first or. second channel. One pairofterminals 74- isconnected Itothe;pairofcodedelectrode structures, 14 and 16 in FIG. 1, theOtherpair of terminals 76 being connected I I to thefirst-named pair 74in crisscrossfashiom'so that first one and thentheother of the pair .ofcoded elec. I trade structures :is. connected. to the second: channeL. II I I A first signalsumrner 62 has its two inputsconnected I I to'the'outputs-oftwc ofthej uncodedelectrode 'struc- I tures, 'l7-L'a'nd118Lwhich are on the left side of the .;.coded; electrode structures, M and16. The output of thefirst signal summer 62 'is'a'single pulse whenproper autocorreiationfunctions are: summed. Asecond signal I summer 64has its two; inputs connectedto theoutputs i I .ofthe other two uncodedelectrode structuresi'iR'and I 18R, respectively. Its output also is asingle-pulse when proper autocorrelation functions are. summed- A timingand .controlapparatus 66, connected to the outputs of the first andsecond signal summers, 62 and 64, controls the time periods during whicha signal from either the first or second channels may be detected. Thetiming and control apparatus 66 would generally only be used if it hadbeen agreed upon in advance that the two signal sources 22 and 24 inFIGS. 2 and 3 would be energized at specific times and for specificintervals of time, for example at one-second intervals.

This alternate energization of the signal sources 22 and 24, could bedone automatically. The timing and control apparatus 66 could includethe means for recognizing a specific sequence of pulses whose purposewould be to actuate a switch which would permit listening in to signalssources 22 or 24 in the desired sequence. Or, a specific sequence ofpulses could alert the listener to flip the switch 70 to the alternateposition.

In FIG. 4-, leads 68 and 69 would go to a special-type demodulator, forexample to a pulse-code modulation (PCM) decoder.

As was the situation with the transmitter 20 shown in FIG. 2, in thereceiver 60 shown in FIG. 4, the pair of coded, interdigitated,electrode structures may be coded according to the two members of aGolay com plementary pair.

A transmitter-receiver used for time-multiplexed communication, maycomprise a single surfaceacoustic-wave device (FIG. 1) which can bereconfirstand then the sume that one signal source is used to input aframe ulse ever kl'sam le interval, and that the second si P Y I gtransceiver at Location I is turned to transmit mode (as per FIG. 2 orFIG-.3)- then the control circuitry automatically switches. back andforth between signal I sources 22 and 24 depending'upon whether theframe 1 I pulse or one ofthe message pulsesis to be imputed to ing.-.

- the surface acoustic; wave device. ill- When the trans ceiver. atLocation l is listening to a similar message generated atsomeotherlocation.,itis turned to the re-- ceive mode (as per FIGLd-'sothatit: can lock onto the frame pulsean imputed bysignal source 22.Then, with synchronization achieved, the receive mode can be I i changedautomatically tothe configuration of'FIG. 5 so that 'thejmessage issynchronously available for decod- I One more received at'lead 69. I I II With the switch arms of switch reversed, the signal emitted by thesecond signal source 24 of FIG. 2 (transmitted from Location No. 2)would now be detected on lead 69, and the signal on lead 68 would beignored. In this instance, the signals +A and B would be received.

Both the first and second signal sources, 22 and 241 of FIG. 2, can betransmitting simultaneously, and yet the receiver 60 shown in FIG. 4could receive either signal, even if the two signal sources are atdifferent locations. Only one signal source, 22 or 2 lof FIG. 2, can belistened to at a time, depending upon the position of the switch arms ofswitch 70.

The first signal source 22 of FIG. 2 causes a signal to be transmitted,on leads 32 and 36, over transmit channels No. l and No. 2. The secondsignal source 36 of FIG. 2, which may be at a different location, alsocauses a signal to be transmitted over the same two channel frequencies,No. l and No. 2. It would be expected that the two transmitted signalswould interfere with each other, but they do not. The receiver 60 ofFIG. l will receive either the signal transmitted by the first signalsource 22 or the second signal source 24, depending upon the position ofthe switch arms of switch 7d.

Of course, the first and second signal sources 22 and 2 could beemitting signals at prearranged time intervals, so that only one signalsource at a time would be transmitting signals. in this case, theconfiguration of FIG. 5 may be also used.

scenario is described in order to demon'-- .strate the flexibilityof'this invention: Assume that two transceiver'units are operating atLocations l. and}, re- I I s'pectively, such that oneis transmitting amessage via I signa source 22 and. the other via signal source 24-; In II this case, they can even transmit'ove-r the same pairof channels'simu'lta'ne ouslytno multiplexingrequired). A

third party at Location :No. 3 desires. to'listen into the I firstsignal source 2120f FIG. 2 (transmitted from Loca-' tion No. l).Referring back to'FlGf 4i,'signal +A would I be-receiv'ed at uppertermirialidand si gnal +8 would be received atilower terminal 7d. Thesignal emitted by the first signal: source22 would be detected at lead66' 1 I I and-aseparate garbage, signal'(to 'beiignio'red) would be i IReferring now to FIG. 5, this figure illustrates another embodiment of areceiver 80 for timemultiplexed communication, also utilizingcomplementary non-interacting codes, including the acoustic surface-wavedevice shown in FIG. 1.

A signal summer 82 has its two inputs connected to the outputs of thetwo coded electrode structures, 14 and 16 in FIG. 1, its outputcomprising multiplexed pulses.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. it is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than specifically described.

l claim:

1. A transmitter for time-multiplexed communication utilizingcomplementary non-interacting codes, comprising:

an acoustic surface-wave device, which provides two parallel signalpropagation paths on its surface, comprising;

a substrate, capable of propagating acoustic surface waves;

a pair of coded interdigitated electrode structures disposed upon thesubstrate, one structure in each of the propagation paths, one structurecoded according to one member of a complementary pair, the otherstructure coded according to the other member of a complementary pair,each coded electrode structure transducing an acoustic wave propagatingin its respective propagation path into an output electrical signalwhich may be transmitted externally of the substrate by means of outputleads; and

two pairs of uncoded interdigitated electrode structures disposed uponthe substrate, one pair in each of the two propagation paths on eachside of the coded electrode structures;

the acoustic surface-wave device having the property that a singleelectrical pulse applied to the uncoded electrode structure results in amultiplepulse {or multi-samplej] electrical output signal at the outputleads;

a first signal source for generating pulses, whose output is connectedto those two of the uncoded electrode structures which are on the sameside of the coded electrode structures; one structure from each pair ofuncoded electrode structures, the signal source generating a stream ofpulses;

a second signal source, also for generating pulses,

whose output is connected to the other two uncoded electrode structures,the second signal source generating a stream of pulses in the intervalsof time when the first signal source is not generating a stream ofpulses;

a signal source switch, whose input terminals are connected to theoutputs of the first and second signal sources and whose outputterminals are connected to, respectively, each pair of the uncodedelectrode structures;

a multiplexing double-pole double-throw switch, for alternatelyswitching an output signal from each of the coded electrical structuresto each of two transmit channels; and

a timing and control apparatus connected to the first and second signalsources and to the signal source and multiplexing switches, whichcontrol (1) the time periods, or intervals, during which the first andsecond signal sources are alternately energized, and (2) the switchingof the arms of the switches from one position to the other insynchronism with the alternate enegization of the signal sources;

with the result that a stream of intermittent pulses from the signalsources becomes a pair of more or less continuous streams of sampleswhich are sent via two transmit channels, with channel exchangeoccurring at intervals determined by the timing control, the streams ofoutput samples concealing coded information.

2. The transmitter according to claim 1, wherein the pair of coded,interdigitated, electrode structures are coded according to the twomembers of a Golay complementary pair.

3. A transmitter for time-multiplexed communication,utilizingcomplementary non-interacting codes, comprising: 1'

an acoustic surface-wave device, which provides two parallel signalpropagation paths on its surface, comprising:

a substrate, capable of propagating acoustic surface waves;

a pair of coded interdigitated electrode structures, disposed upon thesubstrate, one structure in each of the propagation *paths, onestructure coded according to one member of a complementary pair, theother structure coded according to the other'member of a complementarypair, each coded electrode structure transducing an electrical inputpulse into a coded bandpass acoustic signal propagating in itsrespective propagation path towards an uncoded output electrodestructure; and

two pairs of uncoded interdigitated electrode structures disposed uponthe substrate, one pair in each of the two propagation paths on eachside of the coded electrode structures;

the acoustic surface-wave device having the property that a singleelectrical pulse applied to a coded electrode structure results in amulti-sample electrical output signal at the output leads;

a first signal source for generating an intermittent stream of pulses;

a second signal source for'generating pulses in the intervals of timewhen the first signal source is not generating a stream of pulses;

a signal source switch, whose terminals are connected to the outputs ofthe first and second signal sources and whose switch arm is connected toeach of the coded electrode structures;

a multiplexing double-pole double-throw switch, for alternatelyswitching an output signal from each pair of the uncoded electrodestructures to each of two transmit channels, the switch comprising:

one pair of terminals, connected to one of the pairs of uncodedelectrode structures;

the other pair of terminals being connected to the other pair of uncodedelectrode structures; and

the two switch arms being connected to the two transmit channels; and

a timing and control apparatus connected to the first and second signalsources and to the signal source switch, which controls (1) the timeperiods, or intervals, during which the first and second signal l l 12sources are alternately energized, and (2) the coded electrodestructures, one structure from switching of the arms of the switch fromone posieach pair of uncoded electrode structures, and tion to the otherin synchronism with the alternate whose output is a single pulse whenproper autoenergization of the signal sources; correlation functions aresummed; with the result that a stream of intermittent pulses 5 a secondi l Summer, whose two inputs are from the signal sources becomes a pairof more or ne ted to the out ut of the other two uncoded 165$CQfltimlOuS Streams of Samples which are Sent electrode structures, andwhose output is also a sinvia two transmit channels, with channelexchange l pulse when proper autocorrelafion f mi occurring at intervalsdetermined by the timing are d; and Control; the Stream of OutputSamples concealing 0 a timing and control apparatus, connected to theout- Coded P P- puts of the first and second signal summers, which 4-. Areceiver for time-multiplexed communlcatlon, Controls the time periodsduring which a Signal utilizing Compkimemary non'interacting Codes fromeither the first or second signal sources may Pnsmg: be received.

an acoustic surface-wave device, which provides two 5' The receiveraccording to Claim 4, wherein the paralle} S1gnal propaganon paths onSurface pair of coded, interdigitated, electrode structures arecomPnsmgi coded according to the two members of a Golay coma pair ofcoded interdigitated electrode structure s, plementary pain disposedupon the Substrate one Structure 6. A receiver for time-multiplexedcommunication, each of the Propagation paths one Structure utilizingcomplementary non-interacting codes, comcoded according to one member ofa compleprising:

mentary pair, the other structure coded according to the other member ofa complementary pair, each coded electrode structure transducing aninput electrical signal which may be received externally of thesubstrate by means of input leads into an acoustic wave propagating inits respective propagation path; and two pairs of uncoded interdigitatedelectrode structures disposed upon the substrate, one pair in each ofthe two propagation paths on each side of the coded electrodestructures, the acoustic surface-wave device having the property that aparticular pair of coded electrical signals applied to the two codedelectrode structure results in a pair of autocorrelation-like electricaloutput signals at the output lead; a received-signal switch, comprising:

a pair of switch arms, each arm being connectable to a signal receivedfrom a first or second chanan acoustic surface-wave device, whichprovides two parallel signal propagation paths on its surface,comprising:

a substrate, capable of propagating acoustic surface waves;

a pair of coded interdigitated electrode structures, disposed upon thesubstrate, one structure in each of the propagation paths, one structurecoded according to one member of a complementary pair, the otherstructure coded according to the other member of a complementary pair,each coded electrode structure transducing an acoustic wave propagatingin its respective propagation path into an electrical signal which maybe detected externally off the substrate by means of output leads; and

two pairs of uncoded interdigitated electrode structures disposed uponthe substrate, one pair in each of the two propagation paths on eachside nel; one pair of terminals being connected to the pair of the CQdedelectrode Stfllcluffis;

f d d l t d t t the acoustic surface-wave device having the proptheother pair of terminals being connected to the r y hat a pa ticular pairof Coded electrical sigfirst-named pair in criss-cross fashion, so that5 nals applied to the uncoded electrode structure first one and then theother of the pair of coded results in a pair of autocorrelation-likeelectrical electrode structures is connected to the first and outputsignals at the output leads; and then the second channel; a signalsummer whose two inputs are connected to a first signal summer, Whosetwo inputs are conthe outputs ofthe two coded electrode structuresnected to the outputs of two of the uncoded elecand whose outputcomprises multiplexed pulses.

trode structures which are on the same side of the

1. A transmitter for time-multiplexed communication utilizingcomplementary non-interacting codes, comprising: an acousticsurface-wave device, which provides two parallel signal propagationpaths on its surface, comprising; a substrate, capable of propagatingacoustic surface waves; a pair of coded interdigitated electrodestructures disposed upon the substrate, one structure in each of thepropagation paths, one structure coded according to one member of acomplementary pair, the other structure coded according to the othermember of a complementary pair, each coded electrode structuretransducing an acoustic wave propagating in its respective propagationpath into an output electrical signal which may be transmittedexternally of the substrate by means of output leads; and two pairs ofuncoded interdigitated electrode structures disposed upon the substrate,one pair in each of the two propagation paths on each side of the codedelectrode structures; the acoustic surface-wave device having theproperty that a single electrical pulse applied to the uncoded electrodestructure results in a multiple-pulse (or multi-sample) electricaloutput signal at the output leads; a first signal source for generatingpulses, whose output is connected to those two of the uncoded electrodestructures which are on the same side of the coded electrode structures;one structure from each pair of uncoded electrode structures, the signalsource generating a stream of pulses; a second signal source, also forgenerating pulses, whose output is connected to the other two uncodedelectrode structures, the second signal source generating a stream ofpulses in the intervals of time when the first signal source is notgenerating a stream of pulses; a signal source switch, whose inputterminals are connected to the outputs of the first and second signalsources and whose output terminals are connected to, respectively, eachpair of the uncoded electrode structures; a multiplexing double-poledouble-throw switch, for alternately switching an output signal fromeach of the coded electrical structures to each of two transmitchannels; and a timing and control apparatus connected to the first andsecond signal sources and to the signal source and multiplexingswitches, which control (1) the time periods, or intervals, during whichthe first and second signal sources are alternately energized, and (2)the switching of the arms of the switches from one position to the otherin synchronism with the alternate enegization of the signal sources;with the result that a stream of intermittent pulses from the signalsources becomes a pair of more or less continuous streams of sampleswhich are sent via two transmit channels, with channel exchangeoccurring at intervals determined by the timing control, the streams ofoutput samples concealing coded information.
 2. The transmitteraccording to claim 1, wherein the pair of coded, interdigitated,electrode structures are coded according to the two members of a Golaycomplementary pair.
 3. A transmitter for time-multiplexed communication,utilizing complementary non-interacting codes, comprising: an acousticsurface-wave device, which provides two parallel signal propagationpaths on its surface, comprising: a substrate, capable of propagatingacoustic surface waves; a pair of coded interdigitated electrodestructures, disposed upon the substrate, one structure in each of thepropagation paths, one structure coded according to one member of acomplementary pair, the other structure coded according to the othermember of a complementary pair, each coded electrode structuretransducing an electrical input pulse into a coded bandpass acousticsignal propagating in its respective propagation path towards an uncodedoutput electrode structure; and two pairs of uncoded interdigitatedelectrode structures disposed upon the substrate, one pair in each ofthe two propagation paths on each side of the coded electrodestructures; the acoustic surface-wave device having the property that asingle electrical pulse applied to a coded electrode structure resultsin a multi-sample electrical output signal at the output leads; a firstsignal source for generating an intermittent stream of pulses; a secondsignal source for generating pulses in the intervals of time when thefirst signal source is not generating a stream of pulses; a signalsource switch, whose terminals are connected to the outputs of the firstand second signal sources and whose switch arm is connected to each ofthe coded electrode structures; a multiplexing double-pole double-throwswitch, for alternately switching an output signal from each pair of theuncoded electrode structures to each of two transmit channels, theswitch comprising: one pair of terminals, connected to one of the pairsof uncoded electrode structures; the other pair of terminals beingconnected to the other pair of uncoded electrode structures; and the twoswitch arms being connected to the two transmit channels; and a timingand control apparatus connected to the first and second signal sourcesand to the signal source switch, which controls (1) the time periods, orintervals, during which the first and second signal sources arealternately energized, and (2) the switching of the arms of the switchfrom one position to the other in synchronism with the alternateenergization of the signal sources; with the result that a stream ofintermittent pulses from the signal sources becomes a pair of more orless continuous streams of samples which are sent via two transmitchannels, with channel exchange occurring at intervals determined by thetiming control, the stream of output samples concealing codedinformation.
 4. A receiver for time-multiplexed communication, utilizingcomplementary non-interacting codes, comprising: an acousticsurface-wave device, which provides two parallel signal propagationpaths on its surface, comprising: a pair of coded interdigitatedelectrode structures, disposed upon the substrate, one structure in eachof the propagation paths, one structure coded according to one member ofa complementary pair, the other structure coded according to the othermember of a complementary pair, each coded electrode structuretransducing an input electrical signal which may be received externallyof the substrate by means of input leads into an acoustic wavepropagating in its respective propagation path; and two pairs of uncodedinterdigitated electrode structures disposed upon the substrate, onepair in each of the two propagation paths on each side of the codedelectrode structures, the acoustic surface-wave device having theproperty that a particular pair of coded electrical signals applied tothe two coded electrode structure results in a pair ofautocorrelation-like electrical output signals at the output lead; areceived-signal switch, comprising: a pair of switch arms, each armbeing connectable to a signal received from a first or second channel;one pair of terminals being connected to the pair of coded electrodestructures; the other pair of terminals being connected to thefirst-named pair in criss-cross fashion, so that first one and then theother of the pair of coded electrode structures is connected to thefirst and then the second channel; a first signal summer, whose twoinputs are connected to the outputs of two of the uncoded electrodestructures which are on the same side of the coded electrode structures,one structure from each pair of uncoded electrode structures, and whoseoutput is a single pulse when proper autocorrelation functions aresummed; a second signal summer, whose two inputs are connected to theoutputs of the other two uncoded electrode structures, and whose outputis also a single pulse when proper autocorrelation functions are summed;and a timing and control apparatus, connected to the outputs of thefirst and second signal summers, which controls the time periods duringwhich a signal from either the first or second signal sources may bereceived.
 5. The receiver according to claim 4, wherein the pair ofcoded, interdigitated, electrode structures are coded according to thetwo members of a Golay complementary pair.
 6. A receiver fortime-multiplexed communication, utilizing complementary non-interactingcodes, comprising: an acoustic surface-wave device, which provides twoparallel signal propagation paths on its surface, comprising: asubstrate, capable of propagating acoustic surface waves; a pair ofcoded interdigitated electrode structures, disposed upon the substrate,one structure in each of the propagation paths, one structure codedaccording to one member of a complementary pair, the other structurecoded according to the other member of a complementary pair, each codedelectrode structure transducing an acoustic wave propagating in itsrespective propagation path into an electrical signal which may bedetected externally off the substrate by means of output leads; and twopairs of uncoded interdigitated electrode structures disposed upon thesubstrate, one pair in each of the two propagation paths on each side ofthe coded electrode structures; the acoustic surface-wave device havingthe property that a particular pair of coded electrical signals appliedto the uncoded electrode structure results in a pair ofautocorrelation-like electrical output signals at the output leads; anda signal summer whose two inputs are connected to the outputs of the twocoded electrode structures and whose output comprises multiplexedpulses.